Method and apparatus for CSI feedback in CoMP (coordinated multi-point) systems

ABSTRACT

A method and apparatus for coordinating a multi-point wireless transmission between a plurality of geographically separated transmission points and at least one user equipment.

CLAIM OF PRIORITY

This application claims the benefit of U.S. Provisional Application No.61/539,104 filed Sep. 26, 2011 entitled “Method and Apparatus for CSIFeedback in CoMP (Coordinated Multi-Point) Systems” to Runhua Chen,which is incorporated herein by reference in its entirely. Thisapplication also claims the benefit of U.S. Provisional Application No.61/610,728 entitled “Method and Apparatus for CSI Feedback in CoMP(Coordinated Multi-Point) Systems” to Runhua Chen, filed on Mar. 14,2012, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE INVENTION

The technical field of this invention is wireless communication such aswireless telephony.

BACKGROUND OF THE INVENTION

The present embodiments relate to wireless communication systems and,more particularly, to Coordinated Multi-Point (CoMP) transmission inwhich a single mobile unit communicates with plural transmission points.

In legacy wireless cellular systems such as Long Term Evolution (LTE)Rel. 8 to 10, a wireless network includes multiple base stations(eNodeBs, eNBs). Each base station may be configured as a single cellwith its own cell ID. Mobile terminals or user equipment (UE) alwaysconnect to and exchange uplink (UL) data and downlink (DL) data with aconnected cell in single-cell transmission/reception.

CoMP stands for Coordinated Multi-Point transmission. In CoMP multiplegeographically separated transmission points (TP) coordinate with eachother to jointly optimize downlink transmission activities. Theseinclude beam forming vectors, transmission power and/or schedulingdecisions. In contrast to traditional wireless networks without cellcoordination where signals from other transmission points imposeco-channel interference, coordination within multiple TPs allows thesignals to be cooperatively designed to reduce co-channel interference,boost received signal to noise ratio (SNR) and improve cell averagethroughput and cell-edge coverage. A transmission point herein may referto a spatially separated transmission entity such as a base station,cell, macro eNB, pico eNB, femto eNB, remote radio heads, distributedantennas, other wireless transmission entity or a combination of these.

Channel state information reference symbol (CSI-RS) is used in LTE Rel.10 for UE CSI feedback purpose. A UE measures the downlink channel froman eNB transmitter to the UE receiver by using CSI-RS, and reports thechannel state information (CSI) measurement in the uplink. CSI-RS isUE-specific and unprecoded.

In legacy single-cell (or single-point) transmission, UE measures andreports the signal cell CSI of its serving cell. The serving cellconfigures a single-cell CSI-RS resource for downlink measurement. ACSI-RS resource corresponding to one cell may include 1, 2, 4, or 8CSI-RS antenna ports.

SUMMARY OF THE INVENTION

This invention is a technique for coordinate multi-point wirelesstransmission between a plurality of geographically separated points andat least one user equipment.

For multi-point CoMP communication, the UE measures the downlinkwireless propagation channels corresponding to multiple geographicallyseparated transmission points (TP). The network configures multipleCSI-RS resources, each of which is associated with a TP. UE measures thedownlink channel using the multiple configured CSI-RS resources, andreports multiple CSIs in the uplink feedback channel. Each CSI report isdefined as a “CSI-process”, where CSI-process with a lowerCSI-process-index has a higher priority. Multiple CSI-processes can bereported periodically. Each periodic CSI feedback comprises a singleCSI-process. Different CSI-processes are time-domain-multiplexed ondifferent uplink feedback time instances, and are not multiplexed in thesame feedback time instance. If two CSI-processes collide in the timedomain, CSI-process of a higher priority is reported, and CSI-process ofa lower priority is dropped. UE can also feedback multiple CSI-processesin an aperiodic manner, where multiple CSI-processes are reportedsimultaneously. Aperiodic feedback by the UE is triggered by an n-bitCSI-triggering field in an uplink grant transmitted by the network. Eachcodepoint of the n-bit triggering field triggers feedback of a subset ofCST-processes configured by the higher-layer. If UE is configured withCOMP and without carrier aggregation, CSI-processes are ordered bydecreasing CSI-process priority. If UE is configured with CoMP andcarrier aggregation simultaneously, CSI-processes are ordered firstly bydecreasing carrier index, and secondly by decreasing CSI-processpriority.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of this invention are illustrated in thedrawings, in which:

FIG. 1 illustrates an exemplary prior art wireless communication systemto which this application is applicable;

FIG. 2 shows the Evolved Universal Terrestrial Radio Access (E-UTRA)Time Division Duplex (TDD) frame structure of the prior art;

FIG. 3 illustrates an example Coordinated Multi-Point scenario;

FIG. 4 illustrates the process 400 of UE feeding back CSIs andestablishing data communication with eNB.

FIG. 5 illustrates the process of UE aperiodically reporting CSI.

FIG. 6 illustrates an ordering of CSI-processes for a UE configured withCoMP and without carrier aggregation.

FIG. 7 illustrates an ordering of CSI-processes for a UE configured withCoMP and carrier aggregation simultaneously.

FIG. 8 illustrates an ordering of CSI-processes for a UE configured withCoMP on one carrier and without CoMP on another carrier.

FIG. 9 illustrates an ordering of CSI-processes for a UE configured withCoMP and carrier aggregation simultaneously.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary wireless telecommunications network 100. Theillustrative telecommunications network includes base stations 101, 102and 103, though in operation, a telecommunications network necessarilyincludes many more base stations. Each of base stations 101, 102 and 103(eNB) are operable over corresponding coverage areas 104, 105 and 106.Each base station's coverage area is further divided into cells. In theillustrated network, each base station's coverage area is divided intothree cells. Handset or other user equipment (UE) 109 is shown in Cell A108. Cell A 108 is within coverage area 104 of base station 101. Basestation 101 transmits to and receives transmissions from UE 109. As UE109 moves out of Cell A 108 and into Cell B 107, UE 109 may be handedover to base station 102. Because UE 109 is synchronized with basestation 101, UE 109 can employ non-synchronized random access toinitiate handover to base station 102.

Non-synchronized UE 109 also employs non-synchronous random access torequest allocation of up-link 111 time or frequency or code resources.If UE 109 has data ready for transmission, which may be traffic data,measurements report, tracking area update, UE 109 can transmit a randomaccess signal on up-link 111. The random access signal notifies basestation 101 that UE 109 requires up-link resources to transmit the UEsdata. Base station 101 responds by transmitting to UE 109 via down-link110, a message containing the parameters of the resources allocated forUE 109 up-link transmission along with a possible timing errorcorrection. After receiving the resource allocation and a possibletiming advance message transmitted on down-link 110 by base station 101,UE 109 optionally adjusts its transmit timing and transmits the data onup-link 111 employing the allotted resources during the prescribed timeinterval.

Base station 101 configures UE 109 for periodic uplink soundingreference signal (SRS) transmission. Base station 101 estimates uplinkchannel quality information (CQI) from the SRS transmission.

FIG. 2 shows the Evolved Universal Terrestrial Radio Access (E-UTRA)time division duplex (TDD) Frame Structure. Different subframes areallocated for downlink (DL) or uplink (UL) transmissions. Table I showsapplicable DL/UL subframe allocations.

TABLE I Configura- Switch-point Sub-frame number tion periodicity 0 1 23 4 5 6 7 8 9 0  5 ms D S U U U D S U U U 1  5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U DD D D D D 5 10 ms D S U D D D D D D D 6 10 ms D S U U U D S U U DDL CoMP CSI Measurement

CoMP stands for Coordinated Multi-Point Transmission, where multiplegeographically separated transmission points (TP) such as base station,cell, macro eNB, pico eNB, femto eNB, or remote radio heads (RRH),distributed antennas, other wireless transmission entity, or acombination of these, coordinate with each other to jointly optimize thedownlink beamforming signals. A pico eNB is a low-power base stationhaving a smaller cell size for a more limited local coverage than amacro eNB. A femto eNB has an even further limited local coverage,generally in the range of 10 meters. A remote radio head (RRH) is anantenna located remotely from the base station handling the sametransmitter or received signal as the base station. The RRH is coupledto the eNB via a non-air transmission link such as a wired radiofrequency (RF) link or a fiber optic link. The eNB performs the basebandprocessing for all RRHs. In contrast to traditional wireless networkswithout cell coordination where signals from other transmission pointsimpose co-channel interference, coordination within multiple TPs allowsthe signals to be cooperatively optimized in time/frequency/spatialdomain to reduce co-channel interference. This boosts the receivedsignal to noise ratio (SNR) and improves cell average throughput andcell-edge coverage at the UE.

FIG. 3 illustrates an example CoMP scenario 300. Cell 310 includes mainbase station (eNB) 311. Subsidiary cell 320 includes subsidiary basestation (eNB) 321. User equipment (UE) 330 communicates with both basestations. Main eNB 311 communicates with UE 330 via two-way radiofrequency link 312. Subsidiary eNB 321 communicates with UE 330 viatwo-way radio frequency link 322. FIG. 3 illustrates UE 330 within cell310 and not within cell 320, but this is only an example. UE 330 may belocated only within cell 320 and not within cell 310 or within bothcells 310 and 320. The two eNBs 311 and 321 must generally communicatevia a backhaul network 340.

FIG. 4 illustrates the process 400 of the UE initiating communication.At block 401 the UE begins its initialization. This could be triggeredby the UE powering up from an OFF state or the UE first coming withinrange of the corresponding eNB. UE performs cell search, connects to onestrongest cell and obtains its cell ID. In the known art the cell ID canbe determined from primary synchronization signal (PSS) and secondarysynchronization signal (SSS) of the strongest cell. These arecontinuously or periodically transmitted. The network subsequentlyconfigures the UE with CoMP communication where the UE not onlycommunicates with the strongest cell, but also with multiple othercells. This requires UE to measure the multiple channel stateinformation reference signal (CSI-RS) resources of multiple cells. Atthis stage the UE does not know the CSI-RS sequence of other cells,because the UE does not know the cell IDs of other cells involved inCoMP coordination. At block 402 the CSI-RS resource of each cell in COMPcoordination is configured by higher-layer signaling to the UE. Thishigher-layer signaling could be transmitted to the UE by the strongestcell which the UE is synchronized to. Upon determination of the CSI-RSresources, in block 403 the UE measures channel state information on theCSI-RS resource from each eNB. In a COMP scenario there are plural sucheNBs, each with its own CSI-RS resource. At least one of thecommunicating eNBs signals the UE which CSI-RS resources to measure. Inblock 404 the UE uses plural CSI-RS resources to compute a Channel StateInformation (CSI) for each of configured CSI-RS resources. In block 405the UE transmits these CSI measurements. The UE does not control whicheNB receives this signal. The UE transmits this signal and one or moreeNBs receive it.

In block 406 an eNB selects communication parameters for the UE to usein normal communications, which may include the physical resource blocksfor data transmission, modulation and coding scheme, beamformingvectors, and transmission point(s) used for downlink transmission. Thesecommunications parameters may have the UE exchanging UL and DL signalswith one or more of the plural eNBs. The eNB bases this selection on theplural CSI responses from the UE (block 405). In block 407 thecommunicating eNB(s) transmit information that the UE needs to establisha communications link with the eNB. In block 408 the UE establishesnormal communications in accordance with these communication parameters.

DL CoMP CSI Feedback

CSI measurement/feedback is an essential component that plays asignificant role in CoMP operation, for transmission set selection,beamforming computation, multiuser pairing, link adaptation andscheduling. For CoMP the UE feedback (blocks 404 and 405) needs tocontain multiple CSI measurements corresponding to multiple transmissionpoints. In order to do this higher layer signaling configures multipleCSI-RS resources. Each CSI-RS resource corresponds to a uniquesingle-cell CSI-RS pattern. The linkage between each configured CSI-RSresource and each transmission point is configured at the network and istransparent to the UE. The UE measures the CSI-RS of each CSI-RSresource and reports the corresponding CST. Each CSI is defined as a“CSI-process” that reflects a set of recommended transmissionproperties, which may include rank indicator (RI), preceding matrixindicator (PMI), and channel quality indicator (CQI). Rank indicator isthe number of data layers that the UE recommends for downlinktransmission. PMI is an index to a precoding matrix recommended fordownlink data transmission. CQI is an indicator to the signal strengthof the downlink channel, which may be signal-to-noise ratio (SNR) or thesize of a downlink packet. Thus the UE performs measurements on pluralCSI-RS resources for this multiple CSI feedback operation. EachCSI-process can be configured by the higher-layer signaling with aCSI-process-index. Configuration of CSI-process-index is a networkimplementation issue, based for example on UL received signal strengthor on vendor-specific CoMP scheduling algorithm. Additionally, eachCSI-process may be configured with a different priority level. It ispossible that the priority order of a CSI-process is implicitly tied tothe CSI-process-index, where CSI-process with a lower CST-process-indexhas higher priority.

Periodic CSI Feedback

UE feedback of CSI can be configured to be periodic on a specific uplinkphysical channel. In legacy LTE Rel. 8-10 system with single-celloperation, UE can be configured to report single-cell CST periodicallyon the Physical Uplink Control Channel (PUCCH). Periodic CSI feedback onPUCCH is configured with a UE-specific periodicity and time-domainoffset, both in unit of subframe (1 ms). Using the periodicity andoffsets, UE understands which set of uplink subframes shall be used forCSI feedback.

PUCCH is a narrow control channel pipeline. It has a small payload andmust meet a stringent reliability requirement to ensure cell coverage.CSI feedback on PUCCH typically has to be limited to a small payload.For CoMP CSI feedback where multiple CSIs are to be reported, it isundesirable to multiplex several CSI reports in one PUCCH. This isparticular important considering that most UEs receiving COMPtransmission have poor channel geometry, and ensuring cell coverage ischallenging. CSI multiplexing on PUCCH should be avoided in order not tocompromise the uplink control signal coverage. Therefore, each PUCCHshould report a single CSI-process. Feedback of multiple CSI-processeson the PUCCH channel is to be enabled by time-domain multiplexing, whereone PUCCH transmission feeds back one CSI-process. Usually, the networkmay configure different PUCCH reporting periodicities and/or offsets fordifferent CSI-processes, so that they will not be reported in the sameuplink subframe. However if two CSI reports occur in the same uplinksubframe, a collision handling mechanism is needed. In case of CSIcollision on one PUCCH, one CST is reported, and other CSI are dropped.A dropping rule can be defined based on the CSI-process priority.Different CSI-processes may be configured with different priorities bythe higher-layer. If CSI of a higher priority collides with a CSI withlower priority on PUCCH, CSI of higher-priority is reported, and CSI oflower priority is dropped. If priority of CSI-process is implicitly andinversely tied to the CSI-process-index, in the event of CSI collision,CSI-process of a lower CSI-process-index is reported, while CSI-processof a higher CST-process-index is dropped.

Advanced CSI information may be optionally reported by UE. For instance,such advanced CSI feedback includes “inter-CSIRS-resource CSI” whichreflects the spatial correlation between different TPs, in the form of aco-phasing component, or “aggregated CQI” that reflect the SNR value ofsimultaneous transmission from multiple TPs on the same spectrum.

If inter-CSIRS-resource feedback is supported, one PUCCH carriesfeedback defined by either per-CSIRS-resource CSI orinter-CSIRS-resource CSI. PUCCH carrying inter-CSIRS-resource CSI andPUCCH carrying per-CSIRS-resource CST are TDM-multiplexed by configuringdifferent PUCCH periodicities and/or offsets. PUCCH caringinter-CSIRS-resources are TDM-multiplexed for different CSIRS-resources.If PUCCHs carrying per-CSIRS-resource CSI and inter-CSIRS-resource CSIcollide in the time domain, inter-CSIRS-resource CSI is dropped.

If aggregated CSI feedback is chosen, one PUCCH carriesper-CSIRS-resource CST for one CSIRS-resource, or aggregated CSI. PUCCHcarrying inter-CSIRS-resource CSI and PUCCH carrying aggregated CSI areTDM-multiplexed by configuring different PUCCH periodicities and/oroffsets. If PUCCHs carrying per-CSIRS-resource CSI and aggregated CSIcollide in the time domain, per-CSIRS-resource CSI is dropped. If PUCCHcarrying inter-CSIRS-resource CSI and aggregated CSI collide in the timedomain, inter-CSIRS-resource CSI is dropped.

Aperiodic CSI Feedback

UE feedback of CSI can be aperiodic, where the UE receives a triggerfrom the network and transmits the CSI measurement in the uplink. Forinstance, a 1-bit CSI-triggering field in the uplink grant can be usedfor triggering aperiodic CSI report. An uplink grant is a downlinkcontrol signal transmitted by the network which carries uplinkscheduling information including but not limited to the frequencyassignment, modulation and coding scheme. If the 1-bit CSI-triggeringfield in the uplink grant is set to “1”, UE encodes and reports CSI inthe Physical Uplink Shared Channel (PUSCH).

Although multiple CSIs can be reported simultaneously for DL CoMP, it isnot always necessary to report all CSIs all the time. At a particulartime, the network may trigger the UE to report a subset of CSIs that thenetwork considers necessary for downlink scheduling at a particularsystem operation environment. This also helps to reduce the CSI feedbackpayload so that the UE is not required to always feedback the maximumCSI payload. Instead, UE is triggered to only feedback a subset of CSIsdeemed important by the downlink scheduler, resulting in less UE powerconsumption and better uplink coverage.

To achieve this goal, a combination of Radio Resource Control (RRC)configuration and dynamic signaling is used. The uplink grant has ann-bit CSI-triggering field, where each codepoint of the CSI-triggeringfield is used to trigger aperiodic feedback of a subset of CSIs. Thesubset of CSIs corresponding to each codepoint of the n-bit triggeringfield is semi-statically configured by higher-layer signaling. Anembodiment is given in Table II for 2-bit CSI-triggering field.CSI-triggering field is optionally termed as CSI request field.

TABLE II CSI Request for CoMP Value of CSI request field Description‘00’ No aperiodic CSI report is triggered ‘01’ Aperiodic CSI report istriggered for transmission point k ‘10’ Aperiodic CSI report istriggered for a 1^(st) set of transmission points (CSI-RS subsets)configured by higher layers ‘11’ Aperiodic CSI report is triggered for a2^(nd) set of transmission points (CSI-RS subsets) configured by higherlayers

A wireless system may operate on multiple carriers, e.g. carrieraggregation (CA) in LTE Release 10. Herein a carrier refers to a segmentof spectrum that is independently operable for a wireless technology.With carrier aggregation, the network may configure a UE to operate onmultiple adjacent or non-adjacent frequency spectrums simultaneously toincrease the downlink/uplink throughput. This is important to networkoperators with discontinuous frequency spectrum, which is usuallyextremely expensive to acquire. It is beneficial for wireless spectrumre-farming so that when an old wireless system (standard) is no longerdeployed, the old spectrum can be used for operation of a new wirelesssystem jointly with an new carrier. Each carrier is defined as a “cell”or a “CC”, and configured with a different cellID. Under carrieraggregation, a UE is always connected to the network on a primary cell.The primary cell is configured with the lowest cellID. A UE can beoptionally configured to be operable on additional carriers calledsecondary cells, to increase the downlink throughput. Secondary cellscan be turned OFF by the network on a UE-specific manner. Multiple CSIscan be reported for multiple configured cells.

If CoMP and CA are simultaneously configured for a UE, the CSItriggering field in the UL grant may correspond to a combination of DLCCs as well CoMP TP, configured by higher layer. Herein, the uplinkgrant may aperiodically trigger reporting CSI feedback for a subset ofcarriers or CoMP TPs. An example is given in Table III.

TABLE III CSI Request for CoMP with Carrier Aggregation Value of CSIrequest field Description ‘00’ No aperiodic CSI report is triggered ‘01’Aperiodic CSI report is triggered for serving cell c and transmissionpoint k ‘10’ Aperiodic CSI report is triggered for a 1^(st) set ofserving cell c and transmission points k (CSI-RS subsets) configured byhigher layers ‘11’ Aperiodic CSI report is triggered for a 2^(nd) set ofserving cell c and transmission points k (CSI-RS subsets) configured byhigher layers

The uplink grant that a UE is configured to monitor is associated withthe uplink transmission mode that the UE is configured to operate with.In addition to the regular UL grant, a UE is also required to monitor afall-back uplink grant in the common control channel. This fall-backuplink grant has a small payload and has only a 1-bit CSI triggeringfield. The fall-back uplink grant is usually used for fall-backscheduling e.g. when UE is RRC-reconfigured by the network, orexperiences severe channel degradation so that a normal uplink grantcannot be received reliably. The content of the CSI feedback when UEreceives CSI triggering in the fall-back uplink grant may include allCSI-processes, or a subset of the CSI-processes. It is important to notethat maintaining a reliable connection to the network is crucial for theUE in fall-back operation. To this end, the 1-bit triggering fieldshould be used to trigger a single CSI feedback. If a UE is configuredwith CoMP and not with CA, the 1-bit triggering field in the uplinkgrant, when set to “1”, triggers a single CSI report. In one embodiment,the CSI-process with the lowest CSI-process ID, or with the highestpriority, is reported. If a UE is configured with both CoMP and CA, the1-bit triggering field in the fall back uplink grant, triggers a singleCSI feedback for the primary cell. In one embodiment, the CSI-processfor the primary cell with the lowest CSI-process ID is reported.

Encoding of Multiple CSIs on PUSCH

Aperiodic CSI reports are encoded before being transmitted in the uplinkfeedback channel on PUSCH. For instance in LTE, tail-bitingconvolutional code (TBCC) is used for CSI encoding on PUSCH. For CoMP,multiple CSI-processes need to be ordered to form a set of ordered CSIprocesses, encoded and transmitted on PUSCH.

FIG. 5 illustrates the process 500 of the UE ordering the triggered setof CSI-processes. At block 501 the UE receives an uplink granttriggering aperiodic CSI report. At block 502 the UE calculates multipleCSI-processes that are triggered by the n-bit CSI-triggering field inthe uplink grant. At block 503 UE orders the triggered CSI-processes toform a set of ordered CSI-processes. At block 504 UE sends the set ofordered CSI-processes into a channel encoder. At block 505 UE transmitsthe encoded CSI-processes in the uplink feedback channel.

If the UE is configured with CoMP and without CA, CSI processes areordered by decreasing CSI-process priority. In one embodiment, eachCSI-process is configured with a different CSI-process-index, whereCSI-process of a lower CSI-process-index has a higher priority.Correspondingly, CSI-process on PUSCH is ordered by increasingCSI-process indexes.

FIG. 6 illustrates an ordering of CSI-processes for a UE configured withCoMP and without CA. The CSI processes are ordered by increasingCSI-process-indexes, which is equivalent to ordering by decreasingCSI-process priority.

If CoMP and CA are simultaneously configured for a UE, CSI shall beordered according to CSI-process priority and carrier (CC) index. In oneembodiment, the set of CSI-processes triggered by the uplink grant isordered firstly by decreasing CSI-process priority, secondly byincreasing CC index. In another embodiment, the set of CSI-processestriggered by the uplink grant is ordered firstly by increasing CC index,secondly by decreasing CSI-process priority. The second embodiment ispreferred because CSIs corresponding to the same carrier are placed in aconsecutive manner. Once the eNB receives the all CSIs of one carrier,it may immediately start scheduling on that carrier, before CSIs forother carriers are available. This reduces the scheduling latency.Correspondingly, each CSI-process is configured with a differentCSI-process-index, where CSI-process of a lower CSI-process-index has ahigher priority. CSI-processes are then ordered first by increasing CCindex, then by increasing CSI-process-index.

FIG. 7 illustrates an ordering of CSI-processes for a UE configured withCoMP and CA simultaneously. The UE is configured with two downlink cells(CCs), which are CC1 and CC2. The uplink grant triggers 3 CSI-processesto be reported on CC1, and 2 CSI-processes to be reported on CC2. Theordered set of CSI-processes includes the 3 CSI-processes for CC1, byincreasing CSI-process-index, followed by two CSI-processes for CC2, byincreasing CSI-process-index.

A UE may be configured with CoMP on one CC and without CoMP on anotherCC. On the CC where CoMP is configured, multiple CST-processes arereported. On the CC where CoMP is not configured, a single CSI-processis reported. FIG. 8 illustrates an ordering of CSI-processes for a UEconfigured with CoMP on CC1 and without CoMP on CC2. The ordered set ofCSI-processes includes the 3 CSI-processes for CC1, by increasingCSI-process-index, followed by one CSI-process for CC2.

FIG. 9 illustrates an ordering of CSI-processes for a UE configured withCoMP and CA simultaneously, where CSI ordering is firstly by increasingCSI-process-index, secondly by increasing CC index. The UE is configuredwith two downlink cells (CCs), which are CC1 and CC2. The uplink granttriggers 3 CSI-processes to be reported on CC1, and 2 CSI-processes tobe reported on CC2.

What is claimed:
 1. A method, comprising: receiving, at a user equipment(UE), an uplink grant that includes a two-bit channel state information(CSI) triggering field, the two-bit CSI triggering field beingindicative of a selected subset of CSI processes for CSI reporting;determining, by the UE, a first channel quality indicator (CQI)corresponding to a first CSI process based on a first CSI referencesignal (CSI-RS); determining, by the UE, a second CQI corresponding to asecond CSI process based on a second CSI-RS, the first and second CSIprocesses corresponding to a single component carrier, each of the firstand second CSI processes including a respective CSI-Process ID; andtransmitting, by the UE, the first and second CQI based on the two-bitCSI triggering field.
 2. The method of claim 1, wherein a CSI reportingmode is independently configured for the first CSI process and thesecond CSI process.
 3. The method of claim 1, further comprisingtransmitting third CQI corresponding to the first CSI process and fourthCQI corresponding to the second CSI process periodically.
 4. The methodof claim 3, wherein periodicities for reporting the third and fourth CQIcorresponding to the first and second CSI processes, respectively, areindependently configured.
 5. The method of claim 3, wherein transmittingthe third and fourth CQI includes transmitting the third CQI at a firsttime instance, and transmitting the fourth CQI at a second timeinstance.
 6. The method of claim 3, further comprising transmitting CSIcorresponding to a CSI process of a higher priority, and dropping CSIcorresponding to a CSI process of a lower priority when the first andsecond CSI processes are configured to transmit at a same time instance.7. The method of claim 1, wherein transmitting the first and second CQIincludes transmitting the first and second CQI simultaneously at a sametime instance.
 8. The method of claim 1, wherein the selected subset ofthe CSI processes is semi-statically configured by higher-layersignaling.
 9. The method of claim 1, further comprising: ordering thefirst CSI process and the second CSI process to form an ordered set ofCSI processes, where ordering is firstly by increasing cell index, andsecondly by increasing CSI-process priority, and encoding the orderedset of CSI processes, and transmitting the encoded CSI processes in anuplink feedback channel.
 10. The method of claim 1, wherein the firstCSI process is configured with a higher priority than the second CSIprocess.
 11. The method of claim 1, wherein the first CSI process isconfigured with a smaller CSI-process-index than the second CSI process.12. The method of claim 1, further comprising receiving data from atleast two transmission points located at geographically separatelocations.
 13. The method of claim 1, further comprising: receivingfirst data from a first transmission point based on the first CSIprocess; and receiving second data from a second transmission pointbased on the second CSI process.
 14. A base station apparatus,comprising: a transmitter configured to transmit an uplink grant thatincludes a two-bit channel state information (CSI) triggering field, thetwo-bit CSI triggering field being indicative of a selected subset ofCSI processes for CSI reporting; a receiver configured to receive a userequipment (UE) transmission of CSI based on the two-bit CSI triggeringfield, the CSI corresponding to multiple CSI-processes, the multipleCSI-processes corresponding to a single component carrier, each of theCSI-processes being associated with a respective one of a plurality ofChannel State Information (CSI) Reference Signal (CSI-RS) resources,each of the CSI-processes including a respective CSI-Process ID, and atransmitter configured to send a transmission to said UE based on themultiple CSI-processes.
 15. The apparatus of claim 14, wherein themultiple CSI-processes include a first CSI-process and a secondCSI-process.
 16. The apparatus of claim 15, wherein a CSI reporting modeis independently configured for said first CSI-process and said secondCSI-process.
 17. The apparatus of claim 15, wherein said firstCSI-process and said second CSI-process are received periodically. 18.The apparatus of claim 17, wherein said first CSI-process is received ata first time instance, and said second CSI-process is received at asecond time instance.
 19. A user equipment (UE), comprising: a receiverconfigured to receive an uplink grant that includes a two-bit channelstate information (CSI) triggering field, the two-bit CSI triggeringfield being indicative of a selected subset of CSI processes for CSIreporting; and a transmitter configured to transmit channel stateinformation (CSI) based on the two-bit CSI triggering field, the CSIincluding a first channel quality indicator (CQI) corresponding to afirst CSI process and a second channel quality indicator (CQI)corresponding to a second CSI process, the first and second CSIprocesses corresponding to a single component carrier, each of the CSIprocesses including a respective CSI-Process ID, each of the CSIprocesses being associated with a respective one of a plurality of CSIReference Signal (CSI-RS) resources.
 20. The UE of claim 19, wherein aCSI reporting mode is independently configured for the first CSI processand the second CSI process.
 21. The UE of claim 19, wherein thetransmitter is further configured to transmit third CQI corresponding tothe first CSI process and fourth CQI corresponding to the second CSIprocess periodically.
 22. The UE of claim 21, wherein the transmitter isfurther configured to transmit the third CQI at a first time instance,and transmit the fourth CQI at a second time instance.
 23. The UE ofclaim 21, wherein the transmitter is further configured to transmit CSIcorresponding to a CSI process of a higher priority, and drop CSIcorresponding to a CSI process of a lower priority when the first andsecond CSI processes are configured to transmit at a same time instance.24. The UE of claim 19, wherein the UE is further configured to order aset of CSI-processes, and encode the ordered set of CSI-processes,wherein ordering is firstly by increasing cell index, and secondly byincreasing CSI-process priority, and wherein the transmitter is furtherconfigured to transmit the encoded CSI-processes in an uplink feedbackchannel.
 25. The UE of claim 19, wherein the receiver is furtherconfigured to receive first data from a first transmission point basedon the first CSI process, and receive second data on a secondtransmission point based on the second CSI process.
 26. The UE of claim19, wherein periodicities for reporting the third and fourth CQIcorresponding to the first and second CSI processes, respectively, areindependently configured.
 27. The UE of claim 19, wherein thetransmitter is further configured to transmit the first and second CQIsimultaneously at a same time instance.
 28. The UE of claim 19, whereinthe selected subset of the CSI processes is semi-statically configuredby higher-layer signaling.
 29. The UE of claim 19, wherein the first CSIprocess is configured with a higher priority than the second CSIprocess.
 30. The UE of claim 19, wherein the first CSI process isconfigured with a smaller CSI-process-index than the second CSI process.31. The UE of claim 19, wherein the receiver is further configured toreceive data from at least two transmission points located atgeographically separate locations.